NAME

nslookup — query Internet name servers interactively

SYNOPSIS

nslookup

[-option ...] [host-to-find | -[server]]

DESCRIPTION

nslookup is a program to query Internet domain name servers. nslookup has two modes: interactive and non-interactive. Interactive mode allows the user to query name servers for information about various hosts and domains or to print a list of hosts in a domain. Non-interactive mode is used to print just the name and requested information for a host or domain.

ARGUMENTS

Interactive mode is entered in the following cases:

1. when no arguments are given (the default name server will be used),
2. when the first argument is a hyphen (‘-’) and the second argument is the host name or Internet address of a name server.

Non-interactive mode is used when the name or Internet address of the host to be looked up is given as the first argument. The optional second argument specifies the host name or address of a name server.

The options listed under the “set” command below can be specified in the .nslookuprc file in the user's home directory if they are listed one per line. Options can also be specified on the command line if they precede the arguments and are prefixed with a hyphen. For example, to change the default query type to host information, and the initial timeout to 10 seconds, type:

	nslookup -query=hinfo  -timeout=10

INTERACTIVE COMMANDS

Commands may be interrupted at any time by typing a control-C. To exit, type a control-D (EOF) or type exit. The command line length must be less than 256 characters. To treat a built-in command as a host name, precede it with an escape character (‘\’). N.B.: unrecognized command will be interpreted as a host name.

host [server]

Look up information for host using the current default server or using server, if specified. If host is an Internet address and the query type is A or PTR, the name of the host is returned. If host is a name and does not have a trailing period, the default domain name is appended to the name. (This behavior depends on the state of the set options domain, srchlist, defname, and search.)

To look up a host not in the current domain, append a period to the name.

server domain

lserver domain

Change the default server to domain; lserver uses the initial server to look up information about domain, while server uses the current default server. If an authoritative answer can't be found, the names of servers that might have the answer are returned.

root

Changes the default server to the server for the root of the domain name space. Currently, the host ns.internic.net is used. (This command is a synonym for “lserver ns.internic.net”.) The name of the root server can be changed with the “set root” command.

finger [name] [> filename]

finger [name] [>> filename]

Connects with the finger server on the current host. The current host is defined when a previous lookup for a host was successful and returned address information (see the “set querytype=A” command). The name is optional. > and >> can be used to redirect output in the usual manner.

ls [option] domain [> filename]

ls [option] domain [>> filename]

List the information available for domain, optionally creating or appending to filename. The default output contains host names and their Internet addresses. Option can be one of the following:

-t querytype

lists all records of the specified type (see querytype below).

-a

lists aliases of hosts in the domain; synonym for “-t CNAME”.

-d

lists all records for the domain; synonym for “-t ANY”.

-h

lists CPU and operating system information for the domain; synonym for “-t HINFO”.

-s

lists well-known services of hosts in the domain; synonym for “-t WKS”.

When output is directed to a file, hash marks are printed for every 50 records received from the server.

view filename

Sorts and lists the output of previous ls command(s) with more(1).

help

?

Prints a brief summary of commands.

exit

Exits the program.

set keyword[=value]

This command is used to change state information that affects the lookups. Valid keywords are:

all

Prints the current values of the frequently-used options to set. Information about the current default server and host is also printed.

class=value

Change the query class to one of:

IN

the Internet class

CHAOS

the Chaos class

HESIOD

the MIT Athena Hesiod class

ANY

wildcard (any of the above)

The class specifies the protocol group of the information.

(Default = IN; abbreviation = cl)

[no]debug

Turn debugging mode on. A lot more information is printed about the packet sent to the server and the resulting answer.

(Default = nodebug; abbreviation = [no]deb)

[no]d2

Turn exhaustive debugging mode on. Essentially all fields of every packet are printed.

(Default = nod2)

domain=name

Change the default domain name to name. The default domain name is appended to a lookup request depending on the state of the defname and search options. The domain search list contains the parents of the default domain if it has at least two components in its name. For example, if the default domain is CC.Berkeley.EDU, the search list is CC.Berkeley.EDU and Berkeley.EDU. Use the “set srchlist” command to specify a different list. Use the “set all” command to display the list.

(Default = value from hostname(1), /etc/resolv.conf, or LOCALDOMAIN; abbreviation = do)

srchlist=name1/name2/...

Change the default domain name to name1 and the domain search list to name1, name2, etc. A maximum of 6 names separated by slashes (‘/’) can be specified. For example,

set srchlist=lcs.MIT.EDU/ai.MIT.EDU/MIT.EDU

sets the domain to lcs.MIT.EDU and the search list to the three names. This command overrides the default domain name and search list of the “set domain” command. Use the “set all” command to display the list.

(Default = value based on hostname(1), /etc/resolv.conf, or LOCALDOMAIN; abbreviation = srchl)

[no]defname

If set, append the default domain name to a single-component lookup request (i.e., one that does not contain a period).

(Default = defname; abbreviation = [no]defname)

[no]search

If the lookup request contains at least one period but doesn't end with a trailing period, append the domain names in the domain search list to the request until an answer is received.

(Default = search; abbreviation = [no]sea)

port=value

Change the default TCP/UDP name server port to value.

(Default = 53; abbreviation = po)

querytype=value

type=value

Change the type of information query to one of:

A

the host's Internet address.

CNAME

the canonical name for an alias.

HINFO

the host CPU and operating system type.

MINFO

the mailbox or mail list information.

MX

the mail exchanger.

NS

the name server for the named zone.

PTR

the host name if the query is an Internet address; otherwise, the pointer to other information.

SOA

the domain's “start-of-authority” information.

TXT

the text information.

UINFO

the user information.

WKS

the supported well-known services.

Other types (ANY, AXFR, MB, MD, MF, NULL) are described in the RFC-1035 document.

(Default = A; abbreviations = q, ty)

[no]recurse

Tell the name server to query other servers if it does not have the information.

(Default = recurse; abbreviation = [no]rec)

retry=number

Set the number of retries to number. When a reply to a request is not received within a certain amount of time (changed with “set timeout”), the timeout period is doubled and the request is resent. The retry value controls how many times a request is resent before giving up.

(Default = 4, abbreviation = ret)

root=host

Change the name of the root server to host. This affects the “root” command.

(Default = ns.internic.net.; abbreviation = ro)

timeout=number

Change the initial timeout interval for waiting for a reply to number seconds. Each retry doubles the timeout period.

(Default = 5 seconds; abbreviation = ti)

[no]vc

Always use a virtual circuit when sending requests to the server.

(Default = novc; abbreviation = [no]v)

[no]ignoretc

Ignore packet truncation errors.

(Default = noignoretc; abbreviation = [no]ig)

ENVIRONMENT

HOSTALIASES

file containing host aliases

LOCALDOMAIN

overrides default domain

FILES

/etc/resolv.conf

initial domain name and name server addresses

$HOME/.nslookuprc

user's initial options

/usr/share/misc/nslookup.help

summary of commands

DIAGNOSTICS

If the lookup request was not successful, an error message is printed. Possible errors are:

Timed out

The server did not respond to a request after a certain amount of time (changed with “set timeout=value”) and a certain number of retries (changed with “set retry=value”).

No response from server

No name server is running on the server machine.

No records

The server does not have resource records of the current query type for the host, although the host name is valid. The query type is specified with the “set querytype” command.

Non-existent domain

The host or domain name does not exist.

Connection refused

Network is unreachable

The connection to the name or finger server could not be made at the current time. This error commonly occurs with ls and finger requests.

Server failure

The name server found an internal inconsistency in its database and could not return a valid answer.

Refused

The name server refused to service the request.

Format error

The name server found that the request packet was not in the proper format. It may indicate an error in nslookup.

SEE ALSO

resolver(3), resolv.conf(5), named(8)

P.V. Mockapetris, Domain Names - Concepts and Facilities, RFC 1034, Nov 1, 1987.

P.V. Mockapetris, Domain Names - Implementation and Specification, RFC 1035, Nov 1, 1987.

AUTHORS

Andrew Cherenson